1. Field of the Invention
The present invention relates to a laser processing method for forming bores onto a micro lens of a rod-like or a plate-like shape (including a micro lens array having plural lens portions thereon), which bores are provided for inserting optical fibers therein or for adjusting an optical axis thereof.
2. Description of Related Art
Optical communication is able to transfer a large amount of information at high speed, therefore, it has been widely used in various technical fields, for example as main circuits for telephone communication, as circuits for constructing LANs (Local Area Network) or for data transmission among a plurality of devices. A medium for transmitting signals in such optical communications is the optical fiber.
The signal (light) which is generated by a light emitting element, such as a laser diode, for use in optical communications is focused and guided into the optical fiber and transmitted to a signal receiving portion through the optical fiber. At the signal receiving portion, the optical fiber is connected to a light receiving element, such as a photo diode, for reconverting the optical signal into an electric signal.
For the purpose of connecting the optical fiber to the light emitting element or to the light receiving element, a so-called micro lens is used. In more detail, the light generated from the light emitting element can be focused onto the diameter of the optical fiber and introduced thereinto through the micro lens with high efficiency. Additionally, also at the signal receiving side, though the light emitted from the optical fiber has a divergent angle of a certain spread, it can be effectively focused onto a light receiving surface of the light receiving element by use of the micro lens.
It should be noted that for the purpose of introducing the light into the optical fiber and for its emission therefrom, the focal point of the micro lens must be effectively and precisely positioned on the core of the optical fiber.
However, though the diameter of the core of the optical fiber depends on the kind thereof, it is a few or several .mu.m in the case of a single mode optical fiber of quartz, for example. Therefore, a stage device which moves with a very fine accuracy and a relative long time is necessitated for adjusting the core onto the focal point of the lens.
A technology for adjusting the core by using convexo-concave insertion is disclosed for example in Japanese Laid-Open Patent No. Hei 5-333232 (1993), Japanese Laid-Open Patent No. Hei 5-11134 (1993), Japanese Laid-Open Patent No. Hei 7-244222 (1995), Japanese Laid-Open Patent No. Hei 7-248428 (1995) and Japanese Laid-Open Patent No. Hei 2-33105 (1990), etc.
What is disclosed in Japanese Laid-Open Patent No. Hei 5-333232 is, as shown in FIG. 14, that a light sensitive resin is painted on an opposing surface of a plate-like micro lens, and that only the light sensitive resin at the focal point is hardened by exposure via light entering from the lens surface. Thereafter, a projection remains after development and this projection is inserted into a recess portion formed on a front edge of the optical fiber so as to be coupled therewith.
What is disclosed in Japanese Laid-Open Patent No. Hei 5-11134 is that bores for insertion are drilled at core portions of an optical wave-guide, by use of a micro drill, micro end-mill and an electrodeposition grindstone.
What is disclosed in Japanese Laid-Open Patent No. Hei 7-244222 and Japanese Laid-Open Patent No. Hei 7-248428 is that a concave portion is formed by suppressing a heated diamond pressure element of a ring shape, and that into the concave portion is inserted a convex portion which is formed on the front edge surface of the optical fiber.
Further, what is disclosed in Japanese Laid-Open Patent No. Hei 2-33105 is that, by transmitting a monitor light incident into the core layer from an end surface of the core layer of the optical wave-guide and by referencing the monitor light emitted from the other end surface of the optical wave-guide, a CO.sub.2 laser beam is superposed on the monitor light so as to form the concave for inserting the optical fiber in the core portion.
In addition, the method shown in Japanese Laid-Open Patent No. Hei 5-333232 has drawbacks in that the projecting portion made of the light sensitive resin is deteriorated when it is used for a long time or under a high temperature; that the production process takes time and is expensive since it includes many steps, i.e., painting of the light sensitive resin, exposure and development and so on; and further in that undesired refraction occurs on a border or a boundary between the projection and the glass used to construct the micro lens and the optical fiber, since it differs from them in the type of material.
All of the methods disclosed in Japanese Laid-Open No. Patent Hei 5-11134, Japanese Laid-Open No. Patent Hei 7-244222 and Japanese Laid-Open Patent No. Hei 7-248428 are not suitable for mass production since they each require fine machining processes, and further the method disclosed in Japanese Laid-Open Patent No. 2-33105 has a drawback in that it takes a very long time and further has poor productivity since the concave is processed by finely adjusting the position of the micro lens on the stage device by very fine movements, and by ascertaining the focal point by referencing the monitor light.